ERCOT Demand Forecast Accuracy: Error, Bias and Worst Miss, 21 August to 20 September 2026
The day-ahead demand forecast for ERCOT was off by 1.4% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 99% of hours landed within 5% of the reading. Its bias was -0.2%: it ran close to balanced on average. The largest miss was 4,422 MW (5.9%) too high at 25 Aug 2026, 11:00 CDT (UTC-05:00). Dates and times are local (America/Chicago).
Key Facts
- The day-ahead demand forecast for ERCOT was off by 1.4% on average (mean absolute percentage error) over 695 hours from 21 August to 20 September 2026, and 99% of hours landed within 5% of the reading. Its bias was -0.2%: it ran close to balanced on average. The largest miss was 4,422 MW (5.9%) too high at 25 Aug 2026, 11:00 CDT (UTC-05:00).
- Across 53 US grids ranked by average error over their own latest 30 day windows, ERCOT came 1 (1 is the smallest error).
- On average the forecast differed from reported demand by 1,011 MW, against average demand of 71,967 MW.
- The forecast was above reported demand in 45% of compared hours.
Forecast Error at a Glance
695 hours from 21 August to 20 September 2026Average error1.4%
Bias-0.2%
Hours within 5%99%
Worst miss4,422 MW
Average error is the mean absolute percentage gap between the forecast and reported demand. Bias is the signed mean (-129 MW per hour on average): the forecast ran close to balanced on average. The worst miss was 4,422 MW (5.9%) too high at 25 Aug 2026, 11:00 CDT (UTC-05:00): forecast 79,013 MW, reported 74,591 MW.
Source: U.S. Energy Information Administration (EIA). (US Government work, public domain) Data as of 2026-09-20. Accuracy is computed by World Power Monitor from the operator's hourly forecast and reported demand.
Forecast and Reported Demand, Last 7 Days
Local time, to 20 Sept 2026, 20:00 CDT (UTC-05:00)Data to 2026-09-20
| Local hour | Reported demand | Day-ahead forecast |
|---|---|---|
| 13 Sept, 21:00 | 77,206 MW | 74,225 MW |
| 13 Sept, 22:00 | 73,249 MW | 70,448 MW |
| 13 Sept, 23:00 | 69,377 MW | 66,504 MW |
| 14 Sept, 00:00 | 66,013 MW | 65,312 MW |
| 14 Sept, 01:00 | 63,268 MW | 62,543 MW |
| 14 Sept, 02:00 | 61,365 MW | 60,544 MW |
| 14 Sept, 03:00 | 60,103 MW | 59,036 MW |
| 14 Sept, 04:00 | 59,877 MW | 58,513 MW |
| 14 Sept, 05:00 | 60,611 MW | 59,056 MW |
| 14 Sept, 06:00 | 62,166 MW | 60,506 MW |
| 14 Sept, 07:00 | 62,381 MW | 60,860 MW |
| 14 Sept, 08:00 | 64,530 MW | 62,971 MW |
| 14 Sept, 09:00 | 68,549 MW | 67,256 MW |
| 14 Sept, 10:00 | 72,944 MW | 72,134 MW |
| 14 Sept, 11:00 | 77,391 MW | 76,828 MW |
| 14 Sept, 12:00 | 81,369 MW | 81,161 MW |
| 14 Sept, 13:00 | 84,845 MW | 84,773 MW |
| 14 Sept, 14:00 | 85,979 MW | 86,804 MW |
| 14 Sept, 15:00 | 86,162 MW | 87,631 MW |
| 14 Sept, 16:00 | 85,923 MW | 87,769 MW |
| 14 Sept, 17:00 | 85,745 MW | 86,884 MW |
| 14 Sept, 18:00 | 85,400 MW | 84,681 MW |
| 14 Sept, 19:00 | 84,037 MW | 81,778 MW |
| 14 Sept, 20:00 | 81,967 MW | 79,559 MW |
| 14 Sept, 21:00 | 78,675 MW | 76,093 MW |
| 14 Sept, 22:00 | 74,495 MW | 72,134 MW |
| 14 Sept, 23:00 | 70,539 MW | 68,192 MW |
| 15 Sept, 00:00 | 66,843 MW | 66,215 MW |
| 15 Sept, 01:00 | 64,264 MW | 63,228 MW |
| 15 Sept, 02:00 | 62,218 MW | 61,053 MW |
| 15 Sept, 03:00 | 60,947 MW | 59,543 MW |
| 15 Sept, 04:00 | 60,323 MW | 59,040 MW |
| 15 Sept, 05:00 | 60,937 MW | 59,519 MW |
| 15 Sept, 06:00 | 62,080 MW | 61,119 MW |
| 15 Sept, 07:00 | 62,299 MW | 61,337 MW |
| 15 Sept, 08:00 | 64,337 MW | 63,132 MW |
| 15 Sept, 09:00 | 68,297 MW | 67,013 MW |
| 15 Sept, 10:00 | 72,384 MW | 71,454 MW |
| 15 Sept, 11:00 | 76,807 MW | 75,961 MW |
| 15 Sept, 12:00 | 80,986 MW | 80,375 MW |
| 15 Sept, 13:00 | 84,525 MW | 84,234 MW |
| 15 Sept, 14:00 | 86,026 MW | 86,288 MW |
| 15 Sept, 15:00 | 86,111 MW | 87,117 MW |
| 15 Sept, 16:00 | 86,121 MW | 87,416 MW |
| 15 Sept, 17:00 | 85,808 MW | 86,881 MW |
| 15 Sept, 18:00 | 84,948 MW | 85,477 MW |
| 15 Sept, 19:00 | 83,247 MW | 83,199 MW |
| 15 Sept, 20:00 | 81,288 MW | 81,134 MW |
| 15 Sept, 21:00 | 78,155 MW | 77,881 MW |
| 15 Sept, 22:00 | 73,866 MW | 73,683 MW |
| 15 Sept, 23:00 | 69,592 MW | 69,640 MW |
| 16 Sept, 00:00 | 65,965 MW | 67,063 MW |
| 16 Sept, 01:00 | 63,197 MW | 63,887 MW |
| 16 Sept, 02:00 | 60,935 MW | 61,480 MW |
| 16 Sept, 03:00 | 59,776 MW | 59,851 MW |
| 16 Sept, 04:00 | 59,512 MW | 59,227 MW |
| 16 Sept, 05:00 | 60,023 MW | 59,685 MW |
| 16 Sept, 06:00 | 61,276 MW | 61,194 MW |
| 16 Sept, 07:00 | 60,951 MW | 61,422 MW |
| 16 Sept, 08:00 | 63,143 MW | 63,215 MW |
| 16 Sept, 09:00 | 67,022 MW | 67,368 MW |
| 16 Sept, 10:00 | 71,143 MW | 71,990 MW |
| 16 Sept, 11:00 | 75,437 MW | 76,685 MW |
| 16 Sept, 12:00 | 79,533 MW | 81,168 MW |
| 16 Sept, 13:00 | 83,176 MW | 84,930 MW |
| 16 Sept, 14:00 | 84,875 MW | 87,050 MW |
| 16 Sept, 15:00 | 85,779 MW | 88,000 MW |
| 16 Sept, 16:00 | 86,168 MW | 88,246 MW |
| 16 Sept, 17:00 | 85,715 MW | 87,654 MW |
| 16 Sept, 18:00 | 84,256 MW | 85,912 MW |
| 16 Sept, 19:00 | 81,324 MW | 83,411 MW |
| 16 Sept, 20:00 | 78,609 MW | 81,300 MW |
| 16 Sept, 21:00 | 76,293 MW | 77,732 MW |
| 16 Sept, 22:00 | 73,338 MW | 73,498 MW |
| 16 Sept, 23:00 | 69,287 MW | 69,347 MW |
| 17 Sept, 00:00 | 65,721 MW | 65,608 MW |
| 17 Sept, 01:00 | 62,920 MW | 62,708 MW |
| 17 Sept, 02:00 | 60,722 MW | 60,727 MW |
| 17 Sept, 03:00 | 59,001 MW | 59,338 MW |
| 17 Sept, 04:00 | 58,693 MW | 58,876 MW |
| 17 Sept, 05:00 | 59,622 MW | 59,495 MW |
| 17 Sept, 06:00 | 61,221 MW | 61,352 MW |
| 17 Sept, 07:00 | 61,389 MW | 61,630 MW |
| 17 Sept, 08:00 | 63,093 MW | 62,784 MW |
| 17 Sept, 09:00 | 66,698 MW | 66,138 MW |
| 17 Sept, 10:00 | 70,461 MW | 70,202 MW |
| 17 Sept, 11:00 | 74,508 MW | 74,303 MW |
| 17 Sept, 12:00 | 78,032 MW | 78,372 MW |
| 17 Sept, 13:00 | 80,725 MW | 81,748 MW |
| 17 Sept, 14:00 | 82,143 MW | 83,784 MW |
| 17 Sept, 15:00 | 82,698 MW | 84,543 MW |
| 17 Sept, 16:00 | 82,827 MW | 84,484 MW |
| 17 Sept, 17:00 | 82,310 MW | 83,694 MW |
| 17 Sept, 18:00 | 80,340 MW | 81,641 MW |
| 17 Sept, 19:00 | 78,102 MW | 79,046 MW |
| 17 Sept, 20:00 | 76,065 MW | 77,378 MW |
| 17 Sept, 21:00 | 73,926 MW | 74,231 MW |
| 17 Sept, 22:00 | 70,128 MW | 70,428 MW |
| 17 Sept, 23:00 | 66,193 MW | 66,609 MW |
| 18 Sept, 00:00 | 62,703 MW | 62,641 MW |
| 18 Sept, 01:00 | 59,982 MW | 59,888 MW |
| 18 Sept, 02:00 | 58,102 MW | 57,915 MW |
| 18 Sept, 03:00 | 56,706 MW | 56,509 MW |
| 18 Sept, 04:00 | 56,254 MW | 56,146 MW |
| 18 Sept, 05:00 | 56,885 MW | 56,553 MW |
| 18 Sept, 06:00 | 58,535 MW | 58,096 MW |
| 18 Sept, 07:00 | 59,009 MW | 58,444 MW |
| 18 Sept, 08:00 | 60,907 MW | 60,369 MW |
| 18 Sept, 09:00 | 65,084 MW | 64,473 MW |
| 18 Sept, 10:00 | 69,262 MW | 68,904 MW |
| 18 Sept, 11:00 | 73,260 MW | 73,245 MW |
| 18 Sept, 12:00 | 76,582 MW | 77,294 MW |
| 18 Sept, 13:00 | 79,477 MW | 80,921 MW |
| 18 Sept, 14:00 | 81,431 MW | 83,087 MW |
| 18 Sept, 15:00 | 82,563 MW | 84,111 MW |
| 18 Sept, 16:00 | 83,105 MW | 84,408 MW |
| 18 Sept, 17:00 | 82,361 MW | 83,719 MW |
| 18 Sept, 18:00 | 79,708 MW | 81,397 MW |
| 18 Sept, 19:00 | 76,643 MW | 78,297 MW |
| 18 Sept, 20:00 | 74,110 MW | 75,824 MW |
| 18 Sept, 21:00 | 71,187 MW | 72,650 MW |
| 18 Sept, 22:00 | 68,054 MW | 69,116 MW |
| 18 Sept, 23:00 | 64,850 MW | 65,462 MW |
| 19 Sept, 00:00 | 61,775 MW | 63,112 MW |
| 19 Sept, 01:00 | 59,063 MW | 60,114 MW |
| 19 Sept, 02:00 | 56,742 MW | 57,704 MW |
| 19 Sept, 03:00 | 55,113 MW | 55,965 MW |
| 19 Sept, 04:00 | 54,028 MW | 54,949 MW |
| 19 Sept, 05:00 | 53,599 MW | 54,456 MW |
| 19 Sept, 06:00 | 53,752 MW | 54,846 MW |
| 19 Sept, 07:00 | 53,901 MW | 54,873 MW |
| 19 Sept, 08:00 | 56,292 MW | 57,067 MW |
| 19 Sept, 09:00 | 60,786 MW | 61,473 MW |
| 19 Sept, 10:00 | 65,648 MW | 66,026 MW |
| 19 Sept, 11:00 | 70,296 MW | 70,631 MW |
| 19 Sept, 12:00 | 74,264 MW | 74,880 MW |
| 19 Sept, 13:00 | 77,444 MW | 78,412 MW |
| 19 Sept, 14:00 | 80,036 MW | 81,017 MW |
| 19 Sept, 15:00 | 81,942 MW | 82,668 MW |
| 19 Sept, 16:00 | 82,787 MW | 83,334 MW |
| 19 Sept, 17:00 | 81,884 MW | 82,933 MW |
| 19 Sept, 18:00 | 79,676 MW | 80,677 MW |
| 19 Sept, 19:00 | 76,500 MW | 77,380 MW |
| 19 Sept, 20:00 | 74,239 MW | 74,839 MW |
| 19 Sept, 21:00 | 71,194 MW | 71,586 MW |
| 19 Sept, 22:00 | 68,236 MW | 68,303 MW |
| 19 Sept, 23:00 | 65,023 MW | 64,881 MW |
| 20 Sept, 00:00 | 61,856 MW | 62,053 MW |
| 20 Sept, 01:00 | 59,143 MW | 59,381 MW |
| 20 Sept, 02:00 | 56,961 MW | 57,221 MW |
| 20 Sept, 03:00 | 55,427 MW | 55,489 MW |
| 20 Sept, 04:00 | 54,433 MW | 54,267 MW |
| 20 Sept, 05:00 | 53,733 MW | 53,740 MW |
| 20 Sept, 06:00 | 53,692 MW | 53,570 MW |
| 20 Sept, 07:00 | 53,676 MW | 53,456 MW |
| 20 Sept, 08:00 | 55,978 MW | 56,025 MW |
| 20 Sept, 09:00 | 59,914 MW | 60,634 MW |
| 20 Sept, 10:00 | 64,780 MW | 65,449 MW |
| 20 Sept, 11:00 | 69,861 MW | 70,256 MW |
| 20 Sept, 12:00 | 74,626 MW | 74,767 MW |
| 20 Sept, 13:00 | 78,380 MW | 78,627 MW |
| 20 Sept, 14:00 | 81,184 MW | 81,454 MW |
| 20 Sept, 15:00 | 82,867 MW | 83,248 MW |
| 20 Sept, 16:00 | 83,000 MW | 84,103 MW |
| 20 Sept, 17:00 | 81,669 MW | 83,944 MW |
| 20 Sept, 18:00 | 78,296 MW | 81,949 MW |
| 20 Sept, 19:00 | 75,939 MW | 78,873 MW |
| 20 Sept, 20:00 | 74,166 MW | 76,572 MW |
Assumptions
- Only hours with both a forecast and a positive demand reading count (695 of 720 hours in the window). Missing and zero values, and readings under 30% or over 3 times the grid's own median for the window, are treated as reporting faults and left out.
- Error is (forecast minus reported demand) divided by reported demand; average error uses absolute values so high and low misses do not cancel. Bias keeps the sign and does cancel.
- Reported demand is preliminary and may be revised. A 30 day window is a short sample and one heat wave or holiday can move these figures.
- US figures are for the EIA balancing authority or region named on this page. US and European grids are ranked separately.